Dimetallic Imido Complexes of Molybdenum andTungsten with Bridged Bis(η5-cyclopentadienyl) Ligands.

Molecular Structure of[(MoO)2(µ-NtBu)2{µ-(η5-C5H4)2SiMe2}]

Francisco Amor, Pilar Gomez-Sal, Ernesto de Jesus, Avelino Martın,Ana I. Perez, Pascual Royo,* and Amelio Vazquez de Miguel

Departamento de Quımica Inorganica, Universidad de Alcala de Henares,Campus Universitario, 28871 Alcala de Henares, Madrid, Spain

Received December 8, 1995X

New imido and oxo dimetallic complexes of Mo and W with the monobridged or dibridgedbis(cyclopentadienyl) ligands Cp1Cp or Cp2Cp [Cp1Cp ) (η5-C5H4)2SiMe2, Cp2Cp ) (η5-C5H3)2(SiMe2)2] have been synthesized. The Cp2Cp complexes have been obtained as bothcis and trans isomers which differ in the stereodisposition of the two metal fragments withrespect to the Cp2Cp system, the stereochemistry being unchanged in all the reactionsdescribed. Addition of H2NtBu to [(MCl4)2(µ-CpnCp)] (M ) Mo, n ) 1, 2a; n ) 2, 2b; M ) W,n ) 2, 2c) affords the imido M(V) complexes [{M(NtBu)Cl2}2(µ-CpnCp)] (4a-c). Complexes4a,c are oxidized by PCl5 to give [{M(NtBu)Cl3}2(µ-CpnCp)] (5a,c). Both 4a and 5a afford[{MoCl(µ-NtBu)}2(µ-Cp1Cp)] (6) by reduction with sodium amalgam. The differences foundbetween this reaction and the related reductions of the mononuclear Cp analogues arediscussed. Reaction of 6 with HgO affords the oxo complex [{MoO(µ-NtBu)}2(µ-Cp1Cp)] (7).[(MoOCl)2(µ-O)(µ-Cp2Cp)] (3) is obtained by reaction of [{Mo(CO)3Cl}2(µ-Cp2Cp)] with CH3-NO2 or bubbling air through a THF solution of cis-[(MoCl4)2(µ-Cp2Cp)]. The molecularstructure of 7 has been determined by a single-crystal X-ray analysis.

Introduction

The chemistry of imido transition metal complexescontinues to attract considerable attention, and a sub-stantial number of imido cyclopentadienyl complexes ofgroup 6 metals have been reported.1 We reported2-6

previously the isolation of molybdenum and tungstencomplexes with the monobridged and dibridged bis-(cyclopentadienyl) ligands Cp1Cp and Cp2Cp [Cp1Cp )(η5-C5H4)2(SiMe2), Cp2Cp ) (η5-C5H3)2(SiMe2)2]. Herein,we report the results of our studies on the isolation oftheir related dinuclear imido complexes and the signifi-cant differences found between the chemical behaviorof bridged and unbridged cyclopentadienyl systems.Known Cp complexes (Cp ) C5H5 or C5H4Me) relatedto those here reported include [CpMo(NtBu)Cl2], ob-tained by reaction of [CpMoCl4] with NH2

tBu,1,7 [CpMo-(NtBu)Cl3], prepared by treatment of [CpMo(NtBu)2Cl]with HCl8,9 or [CpMo(NtBu)2Cl] with Cl2,7 and [CpMo-

(NtBu)ClL], prepared by reduction of [CpMo(NtBu)Cl2]in the presence of free ligands.1,7

Results and Discussion

Preparative Methods. Paramagnetic (µeff ≈ 2.0-2.2 µB) tetrahalo complexes cis- and trans-[(MCl4)2(µ-Cp2Cp)] (M ) Mo (2b), M ) W (2c)) were prepared byoxidation of [{M(CO)3Cl}2(µ-Cp2Cp)] (1b,c) with PCl5 aschlorinating agent,10 as we have already reported2 forthe preparation of the related monobridged Mo complex2a (Scheme 1). Treatment of cis-1b with CH3NO2 intoluene results in complete decarbonylation and forma-tion of the oxo complex [(MoOCl)2(µ-O)(µ-Cp2Cp)] (3)after heating the mixture at 80 °C overnight. Alterna-tively, complex 3 can be obtained by bubbling airthrough a THF solution of complex cis-2b for 1 h. Thed1-d1 complex 3 is diamagnetic, as are [(CpMoOX)2(µ-O)] (Cp ) η-C5H5, C5Me, X ) Cl,11 I12).Addition of 6 equiv of NtBuH2 to the halo complexes

2 affords the imido compounds [{M(NtBu)Cl2}2(µ-Cp-nCp)] (4a-c), by a reaction similar to that used for thesynthesis of the related C5H5 complexes.7 Compounds4a,c could not be isolated, although the resulting brownsolids can be used as starting materials for furtherreactions. Oxidation of complexes 4a,c with PCl5 givesthe M(VI) complexes [{M(NtBu)Cl3}2(µ-CpnCp)] (n ) 1,M ) Mo (5a); n ) 2, M ) W (5c)). Reaction of 4b with

X Abstract published in Advance ACS Abstracts, March 15, 1996.(1) Green, M.; Konidaris, P. C.; Mountford, P. J. Chem. Soc., Dalton

Trans. 1994, 2851 and references therein.(2) Gomez-Sal, P.; de Jesus, E.; Perez, A. I.; Royo, P.Organometallics

1993, 12, 4633.(3) Amor, F.; Gomez-Sal, P.; de Jesus, E.; Royo, P.; Vazquez de

Miguel, A. Organometallics 1994, 13, 4322.(4) Galakhov, M. V.; Gil, A.; de Jesus, E.; Royo, P. Organometallics

1995, 14, 3746.(5) Amor, F.; de Jesus, E.; Royo, P.; Vazquez de Miguel, A. Inorg.

Chem. 1996, in press.(6) Amor, F.; de Jesus, E.; Perez, A. I.; Royo, P.; Vazquez de Miguel,

A. Organometallics 1996, 15, 365.(7) Green, M. L. H.; Konidaris, P. C.; Mountford, P.; Simpson, S. J.

J. Chem. Soc., Chem. Commun. 1992, 256.(8) Sundermeyer, J.; Radius, U.; Burschka, C. Chem. Ber. 1992, 125,

2379.(9) Radius, U.; Sundermeyer, J. Chem. Ber. 1992, 125, 2183.

(10) Murray, R. C.; Blum, L.; Liu, A. H.; Schrock, R. R. Organome-tallics 1985, 4, 953.

(11) Umakoshi, K.; Isobe, K. J. Organomet. Chem. 1990, 395, 47.Bottomley, F.; Ferris, E. C.; White, P. S.Organometallics 1990, 9, 1166.Bottomley, F.; Boyle, P. D.; Chen, J. Organometallics 1994, 13, 370.

(12) Bunker, M. J.; Green, M. L. H. J. Chem. Soc., Dalton Trans.1981, 847.

2103Organometallics 1996, 15, 2103-2107

0276-7333/96/2315-2103$12.00/0 © 1996 American Chemical Society

PCl5 gives an unresolved mixture of compounds. Re-duction of the Mo(V) {[Mo(NtBu)Cl2}2(µ-Cp1Cp)] (4a) orthe Mo(VI) [{Mo(NtBu)Cl3}2(µ-Cp1Cp)] (5a) complexeswith the appropriate stoichiometric amounts of sodiumamalgam affords the Mo(IV) derivative [{MoCl(µ-NtBu)}2(µ-Cp1Cp)] (6) (Scheme 2) in which two imidogroups are bridging both metal centers (see StructuralStudy). Compound 6 does not react either by additionof ligands (CNtBu, ethylene, 2-butyne, or CO) or byreduction of 4a or 5a in the presence of free ligands,and therefore the dimetallic complexes [{Mo(NtBu)-ClL}2(µ-Cp1Cp)] could not be obtained, in contrast withthe related Cp complexes.1,7 This behavior indicatesthat the bridged Cp1Cp system seems to favor theformation of the more stable chelated Mo(µ-NtBu)2Moring in relation to the unbridged Cp systems. Unfor-tunately, we were not able to obtain the analogue withthe dibridged Cp2Cp ligand to compare the behavior ofboth types of bridged systems.Reaction of 6 with HgO in THF affords the oxo com-

plex [(MoO)2(µ-NtBu)2(µ-Cp1Cp)] (7). This complex shows

a cis disposition of the cyclopentadienyl rings along theMo-Mo bond imposed by the Cp1Cp bridge whereas atrans arrangement has been proposed for the relatedCp complexes [{MoO(µ-NR)(η5-C5H4Me)}2] (R ) tBu,13Ph14). The molecular structure of 7 is discussed below.Structural Study. Spectroscopic data for all the new

complexes are given in the Experimental Section. Allthe diamagnetic complexes have been characterized by1H NMR, and their spectra show typical resonances forthe cyclopentadienyl ring in the range 5.1-7.4 ppm andfor SiMe2 in the range -0.5 to 1.1 ppm. The ringprotons appear as two groups of resonances correspond-ing to the AA′ and BB′ parts of an AA′BB′ spin system,for the monobridged Cp1Cp complexes 5a, 6, and 7, andcorresponding to the A and BB′ parts of an ABB′ spinsystem, for the dibridged Cp2Cp complexes 5c. The 13C-{1H} NMR data confirm that the four R- and the four/

(13) Green, M. L. H.; Konidaris, P. C.; Mountford, P. J. Chem. Soc.,Dalton Trans. 1994, 2975.

(14) Green, M. L. H.; Hogarth, G.; Konidaris, P. C.; Mountford, P.J. Chem. Soc., Dalton Trans. 1990, 3781.

Scheme 1

Scheme 2

2104 Organometallics, Vol. 15, No. 8, 1996 Amor et al.

two â-carbons and their substituents are chemicallyequivalent at room temperature in complexes 5-7. Thischemical equivalency implies the existence of two planesof symmetry (one defined by the SiMe2 groups, and theother perpendicular to it and passing through the metalcenters) in the structure of a rigid molecule or in theaverage structure of a fluxional molecule. The tBugroups of the imido ligands appear as singlets at ca. 1.5ppm for the terminal ligands and at ca. 1.7 ppm for thebridging ligands.The 13C CP-MAS spectrum of [{Mo(NtBu)Cl3}2(µ-η5:

η5-Cp1Cp)] (5a), slightly soluble in common organicsolvents, is in agreement (see Experimental Section)with the lower symmetry expected for the supressionin the solid state of some of the dynamic processesoccurring in solution. The 1H NMR spectrum of the oxocomplex 3 shows four resonances for the SiMe2 groups.The cyclopentadienyl protons appear as two groups ofresonances that are centered at 6.37 and 7.18 ppm. Thepattern of these resonances is more complicated thanexpected for an ABB′ spin system, and they are assignedto an ABC spin system in which the B and C parts,corresponding to the R and R′ protons, have a similarchemical shift. The absence of a plane of symmetrypassing through the Cp centroids and Mo atoms or of aC2 axis is confirmed by the 13C{1H} NMR spectrum thatshows four resonances for the Me2Si groups and fiveresonances for the cyclopentadienyl ring carbons. Thesedata are in agreement with the structure proposed for3, characterized by a linear bridging oxygen atom, asfound for other d1-d1 and d0-d0 Mo-O-Mo sys-tems,11,12,15 and by a cis disposition of the Cl and Oatoms through the Mo2(µ-NtBu)2 plane.Crystal Structure of 7. The molecular structure of

7 based on the X-ray structural analysis is shown inFigure 1 with the numbering scheme employed. Im-portant bond distances and angles are listed in Table1. Two independent molecules exist in the asymmetricunit of the unit cell of 7. Molecule A is defined as thatcontaining Mo(1) and Mo(2), and molecule B, as thatcontaining Mo(3) andMo(4). Molecule B parameters aregiven in brackets. The molecular parameters for A andB are very similar.The molecular structure of 7 comprises a dinuclear

system with the two Mo atoms bridged by one Cp1Cpand two NtBu ligands. Each Mo atom has a “three-legged piano stool” geometry, where the legs are formedby two bridging NtBu groups and one oxygen atom. Ifthe centroid of each Cp ring is taken as a coordinationsite, the angles around Mo between this point and thelegs range from 113 to 126° and between legs range from94.0 to 94.6° (N-Mo-N angles) and from 104.5 to 105.6°(O-Mo-N angles).We have reported previously2 that the angles θ1 and

θ2 between the cp(1)-Si-cp(2) plane and the cp(1)-Mo-(1) and cp(2)-Mo(2) axis, respectively (Chart 1; cp )centroid of the cyclopentadienyl ring) can be used torationalize the arrangement of the metal centers in thestructures of bimetallic Cp1Cp complexes. In complex1a, where metal-metal bond and ligand bridges (otherthan the Cp1Cp bridge) are absent, the values of the θ

angles are close to 180°, moving the two metal centersapart.2 In complexes with metal-metal bonds or ligand

(15) Gomez-Sal, P.; de Jesus, E.; Royo, P.; Vazquez de Miguel, A.;Martınez-Carrera, S.; Garcıa-Blanco, S. J. Organomet. Chem. 1988,353, 191. Faller, J. W.; Ma, Y. J. Organomet. Chem. 1988, 353, 59.Leoni, O.; Pasquali, M.; Salsini, L.; di Bugno, C.; Braga, D.; Sabatino,P. J. Chem. Soc., Dalton Trans. 1989, 155. Rheingold, A. L.; Harper,J. R. J. Organomet. Chem. 1991, 403, 335.

Figure 1. Perspective view of the molecular structure of[{MoO(µ-NtBu)}2(µ-Cp1Cp)] (7) with the atom-numberingscheme.

Table 1. Selected Bond Distances (Å) and BondAngles (deg) for 7

molecule A molecule B

DistancesMo(1)-Mo(2) 2.634(1) Mo(3)-Mo(4) 2.630(1)Mo(1)-O(1) 1.703(6) Mo(3)-O(3) 1.707(7)Mo(2)-O(2) 1.696(6) Mo(4)-O(4) 1.707(6)Mo(1)-N(1) 1.945(7) Mo(3)-N(3) 1.930(7)Mo(1)-N(2) 1.939(7) Mo(3)-N(4) 1.941(8)Mo(2)-N(1) 1.938(7) Mo(4)-N(3) 1.920(7)Mo(2)-N(2) 1.929(8) Mo(4)-N(4) 1.957(7)Mo(1)-cp(1)a 2.096 Mo(3)-cp(3)a 2.126Mo(2)-cp(2)a 2.115 Mo(4)-cp(4)a 2.107Si(1)-C(11) 1.840(9) Si(2)-C(31) 1.864(10)Si(1)-C(21) 1.864(10) Si(2)-C(41) 1.850(9)Si(1)-C(51) 1.88(2) Si(2)-C(61) 1.81(2)Si(1)-C(52) 1.84(2) Si(2)-C(62) 1.89(2)N(1)-C(71) 1.508(12) N(3)-C(91) 1.486(12)N(2)-C(81) 1.487(13) N(4)-C(101) 1.458(13)

Anglescp(1)a-Mo(1)-O(1) 119.0 cp(3)a-Mo(3)-O(3) 121.1cp(1)a-Mo(1)-Mo(2) 125.6 cp(3)a-Mo(3)-Mo(4) 124.6cp(1)a-Mo(1)-N(1) 114.7 cp(3)a-Mo(3)-N(3) 115.2cp(1)a-Mo(1)-N(2) 114.7 cp(3)a-Mo(3)-N(4) 112.7cp(2)a-Mo(2)-O(2) 120.7 cp(4)a-Mo(4)-O(4) 120.4cp(2)a-Mo(2)-Mo(1) 125.0 cp(4)a-Mo(4)-Mo(3) 125.5cp(2)a-Mo(2)-N(1) 114.7 cp(4)a-Mo(4)-N(3) 115.7cp(2)a-Mo(2)-N(2) 113.7 cp(4)a-Mo(4)-N(4) 113.2O(1)-Mo(1)-Mo(2) 115.4(3) O(3)-Mo(3)-Mo(4) 114.3(3)O(2)-Mo(2)-Mo(1) 114.3(3) O(4)-Mo(4)-Mo(3) 113.9(3)N(1)-Mo(1)-N(2) 94.0(3) N(3)-Mo(3)-N(4) 94.5(3)N(1)-Mo(2)-N(2) 94.6(3) N(3)-Mo(4)-N(4) 94.3(3)Mo(1)-N(1)-Mo(2) 85.4(3) Mo(3)-N(3)-Mo(4) 86.2(3)Mo(1)-N(2)-Mo(2) 85.8(3) Mo(3)-N(4)-Mo(4) 84.9(3)C(11)-Si(1)-C(21) 113.3(4) C(31)-Si(2)-C(41) 113.2(4)C(51)-Si(1)-C(52) 112.6(8) C(61)-Si(2)-C(62) 112.2(8)C(71)-N(1)-Mo(1) 138.1(6) C(91)-N(3)-Mo(3) 133.9(6)C(71)-N(1)-Mo(2) 135.0(6) C(91)-N(3)-Mo(4) 137.2(6)C(81)-N(2)-Mo(1) 135.7(7) C(101)-N(4)-Mo(3) 135.1(6)C(81)-N(2)-Mo(2) 135.0(6) C(101)-N(4)-Mo(4) 134.9(6)

a cp(1) is the centroid of C(11)-C(15); cp(2) is the centroid ofC(21)-C(25); cp(3) is the centroid of C(31)-C(35); cp(4) is thecentroid of C(41)-C(45).

Imido Complexes of Molybdenum and Tungsten Organometallics, Vol. 15, No. 8, 1996 2105

bridges, the θ angles are decreased to accommodate themetal-metal distance. Thus, in 7 these angles are closeto 0°, being 0.8 and -1.4° [4.6 and -4.7°], as expected2for a Mo-Mo distance as short as 2.63 Å. The distancebetween metals does not completely determine thestereodisposition of the Mo(Cp1Cp)Mo system becausea given distance can be achieved in both a cisoid ortransoid arrangement. Complex 7 shows a cisoid ar-rangement imposed by the double imido bridge, result-ing in a very symmetrical structure. Thus, Si(1), Mo(1),Mo(2), C(11), and C(21) [Si(2), Mo(3), Mo(4), C(31), andC(41)] define a vertical plane that also contains theoxygen atoms, with a maximum deviation of 0.053(9) Åfor O(3).The Mo-Mo distance of 2.634(1) [2.630(1)] Å is

slightly shorter than those reported for [{(η5-C5H4Me)-Mo(NPh)}2(µ-NPh)2] [2.717(1) Å],14 [{(η5-C5H4Me)MoO}2-(µ-O)(µ-NPh)] [2.662(1) Å],16 [{(η5-C5H4Me)MoO}2(µ-NPh)2] [2.691(1) Å]),16 and [{(η5-C5H4Me)MoO}2(µ-N(C6F5))2] [2.686(1) Å].17 The Mo-N(bridge) and Mo-Odistances are typical for these complexes (1.92-1.94 and1.70-1.71 Å, respectively). It has been observed thatcomplexes of the form [(CpMoX)2(µ-Y)2] (X, Y ) O andNPh) have planar Mo2(µ-Y)2 cores when the Cp ligandsare trans and puckered Mo2(µ-Y)2 cores with the µ-Yligands folded toward the rings when the Cp ligandsare cis.14,16-18 The coordination around the µ-N atomsis always planar in these complexes. In contrast, theMo(µ-N)2Mo core is planar in the cis complex 7, themaximum deviation from planarity being -0.04 Å witha dihedral angle between the two Mo2(µ-N) planes of176.2(3)° [176.5(3)°] and with the N atoms slightlyfolded away from the Cp1Cp system. The coordinationaround the µ-N atoms in 7 is slightly pyramidalized,the distances from the C(bonded to N) to the Mo2N2plane being in the range 0.336(7)-0.50(1) Å. Thesedifferences between 7 and other [(CpMoX)2(µ-Y)2] sys-tems may be due to the greater steric hindrance createdby the tBu and the bridged Cp1Cp compared with thePh and unbridged Cp that moves the N atoms and thetBu groups away from the Cp1Cp system.

Experimental Section

Reagents and General Techniques. All reactions werecarried out in dried Schlenk tubes under an atmosphere ofargon or nitrogen, and manipulations were carried out usingsyringes or cannulae through Subaseals. Solvents were dried

and distilled under nitrogen: CH2Cl2 over P4O10; diethyl etherand tetrahydrofuran from sodium benzophenone ketyl; hexane,pentane, and toluene from sodium. Unless otherwise stated,reagents were obtained from commercial sources and used asreceived. IR spectra were recorded in Nujol mulls for solidsor in CaF2 cells for solutions, over the range 4000-200 cm-1

on a Perkin-Elmer 583 spectrophotometer. IR data are givenin cm-1. The 1H and 13C NMR spectra were recorded at 299.95and 75.43 MHz, respectively, on a Varian Unity 300 spectrom-eter; chemical shifts, in ppm, are positive downfield relativeto external SiMe4; coupling constants are in Hz. C, H, and Nanalyses were performed with a Perkin-Elmer 240-B instru-ment. The chloride analyses were performed according to ref19. ESR spectra were recorded on a Varian Unity E-12spectrometer. Magnetic susceptibilities were measured in aBruker B-E15 magnetic balance. Mass spectra were recordedin a Hewlett-Packard 5988A spectrometer.Starting Materials. Complexes 1b,3 1c,6 and 2a2 were

prepared according to reported methods.Preparation of cis-[(MoCl4)2{µ-(η5-C5H3)2(SiMe2)2}] (cis-

2b). cis-1b (1.88 g, 2.79 mmol) and PCl5 (2.33 g, 11.2 mmol)were suspended in toluene (50 mL) and stirred overnight at80 °C. The mixture was filtered and the residue washed withcold CH2Cl2. Complex cis-2b was obtained as a purple solid(1.80 g, 90%). Anal. Calcd for C14H18Si2Cl8Mo2: C, 23.4; H,2.5. Found: C, 24.0; H, 3.0. ESR (THF): g ) 1.92.Preparation of trans-2b. This complex was obtained as

a purple solid (1.93 g, 85%) from trans-1b (2.14 g, 3.18 mmol)and PCl5 (3.0 g, 14.4 mmol) in toluene (60 mL) by theprocedure described for cis-2b. Anal. Calcd for C14H18Si2Cl8-Mo2: C, 23.4; H, 2.5. Found: C, 23.0; H, 2.5. ESR (THF): g) 1.92.Preparation of cis-[(WCl4)2{µ-(η5-C5H3)2(SiMe2)2}] (cis-

2c). This complex was obtained as a brown solid (1.23 g, 73%)from cis-1c (1.60 g, 1.88 mmol) and PCl5 (1.57 g, 7.54 mmol)in CH2Cl2 (70 mL) by the procedure described for cis-2b. Anal.Calcd for C14H18Si2Cl8W2: C, 18.8; H, 2.0. Found: C, 18.8; H,2.1. ESR (THF): g ) 1.92.Preparation of trans-2c. The complex was obtained as a

brown solid (0.24 g, 42%) from trans-1c (0.54 g, 0.64 mmol)and PCl5 (0.53 g, 2.5 mmol) in CH2Cl2 (50 mL) by the proceduredescribed for cis-2b. Anal. Calcd for C14H18Si2Cl8W2: C, 18.8;H, 2.0. Found: C, 19.2; H, 2.0. ESR (THF): g ) 1.92.Preparation of [(MoOCl)2(µ-O){µ-(η5-C5H3)2(SiMe2)2}]

(3). From cis-1b. A mixture of cis-1b (0.59 g, 0.88 mmol)and CH3NO2 (0.10 mL, 1.8 mmol) was heated overnight intoluene (50 mL) at 80 °C. The solution changed from red topurple. After filtration, the solvent was completely removedin vacuo and the residue dissolved in CH2Cl2 (5 mL). Complex3 (0.28 g, 58%) was precipitated with pentane (50 mL) as apurple solid.From cis-2b. An air stream was bubbled through a

solution of cis-2b (0.40 g, 0.56 mmol) in THF (100 mL) for 1 h.After evaporation, the residue was dissolved in CH2Cl2 (25 mL)and dried over Na2SO4. The solvent was partially evaporated(up to ca. 15 mL), and complex 3 (0.15 g, 48%) was precipitatedby addition of pentane (50 mL). Anal. Calcd for C14H18-O3Si2Cl2Mo2: C, 30.4; H, 3.3; Cl, 12.8. Found: C, 30.8; H, 3.7,Cl, 12.0. MS: m/e 556 (M+). IR (Nujol): ν(ModO) 937 s; ν-(Mo-O-Mo) 786 s. 1H NMR (CDCl3): δ 7.18, 6.37 (A and BCparts of an ABC spin system, 6 H, C5H3), 0.75 (s, 3 H, SiMe2),0.64 (s, 3 H, SiMe2), 0.44 (s, 3 H, SiMe2), 0.42 (s, 3 H, SiMe2).13C{1H} NMR (CDCl3): δ 130.8 (s, C5H3 â, from 13C NMR:1J(CH) ) 180), 124.8 (s, C5H3 ipso), 122.1 (s, C5H3 R, from 13CNMR: 1J(CH) ) 178), 117.0 (s, C5H3 ipso), 105.7 (s, C5H3 R),1.0 (s, SiMe2), -3.4 (s, SiMe2), -4.5 (s, SiMe2), -5.4 (s, SiMe2).Preparation of cis-[{Mo(NtBu)Cl2}2{µ-(η5-C5H3)2(Si

Me2)2}] (cis-4b). NtBuH2 (0.44 mL, 4.17 mmol) was addedover a suspension of cis-2b (0.50 g, 0.69 mmol) in toluene (50mL). The solution changed from purple to yellow-brown. Themixture was stirred for 7 h and then was filtered. The solvent

(16) Fletcher, J.; Hogarth, G.; Tocher, D. A. J. Organomet. Chem.1991, 403, 345.

(17) Fawcett, J.; Holloway, J. H.; Hope, E. G.; Russell, D. R.;Saunders, G. C.; Atherton, M. J. J. Organomet. Chem. 1994, 464, C20.

(18) Couldwell, C.; Prout, K. Acta Crystallogr., Sect. B 1978, 34, 933.Arzoumanian, H.; Baldy, A.; Pierrot, M.; Petrignani, J.-F. J. Orga-nomet. Chem. 1985, 294, 327. (19) White, D. C. Mikrochim. Acta 1961, 449.

Chart 1

2106 Organometallics, Vol. 15, No. 8, 1996 Amor et al.

was completely removed in vacuo. The brown solid obtainedwas extracted into toluene (30 mL), and the solvent wascompletely removed in vacuo to give a brown solid (0.38 g,76%). Anal. Calcd for C22H36N2Si2Cl4Mo2: C, 36.8; N, 3.9; H,5.0. Found: C, 37.2; N, 3.8; H, 4.9. ESR (toluene): g ) 1.98.Preparation of trans-4b. This complex was obtained as

a brown solid (0.16 g, 70%) from trans-2b (0.23 g, 0.32 mmol)and NtBuH2 (0.20 mL, 1.92 mmol) by the procedure describedfor the cis isomer. Anal. Calcd for C22H36N2Si2Cl4Mo2: C, 36.8;N, 3.9; H, 5.0. Found: C, 36.9; N, 3.9; H, 5.2 ESR (toluene):g ) 1.98.Preparation of [{Mo(NtBu)Cl3}2{µ-(η5-C5H4)2SiMe2}] (5a).

Solid PCl5 (1.20 g, 5.77 mmol) was added to a solution of 4a(2.50 g, 3.77 mmol) in toluene (40 mL). The mixture wasstirred for 14 h at room temperature. The yellow precipitatewas isolated by filtration, washed with CH2Cl2/pentane (1:3),and dried in vacuo (2.53 g, 92%). Anal. Calcd for C20H32-N2SiCl6Mo2: C, 32.8; H, 4.4; N, 3.8. Found: C, 32.9; H, 4.35;N, 3.4. 1H NMR (acetone-d6): δ 7.40, 6.86 (AA′ and BB′ partsof an AA′BB′ spin system, 4 H, C5H4), 1.54 (s, 9 H, NtBu), 0.81(s, 3 H, SiMe2). 13C CP-MAS: δ 153.6 (s, C5H4), 149.2 (s, C5H4),141.7 (s, C5H4), 128.7 (s, C5H4), 117.7 (s, C5H4), 106.3 (s, C5H4),102.8 (s, C5H4), 85.7 (s, NCMe3), 28.8 (S, NCMe3), 26.1 (s,NCMe3), -2.7 (s, SiMe2), -4.1 (s, SiMe2).Preparation of cis-[{W(NtBu)Cl3}2{µ-(η5-C5H3)2(SiMe2)2}]

(cis-5c). NtBuH2 (0.30 mL, 2.3 mmol) was added to asuspension of cis-2c (0.42 g, 0.47 mmol) in toluene (50 mL),and the mixture was stirred for 7 h. Then, PCl5 (0.20 g, 0.94mmol) was added and stirring was continued overnight. Afterfiltration, the precipitate was extracted with CH2Cl2 (2 × 25mL), and solvent was completely removed from the yellowsolution in vacuo. The solid was recrystallized by dissolutionin CH2Cl2 (20 mL) and precipitation with hexane (75 mL) at-40 °C to afford cis-5c (0.26 g, 57%) as a yellow solid. Anal.Calcd for C22H36N2Si2Cl6W2: C, 27.4; N, 2.9; H, 3.8. Found:C, 27.6; N, 3.0; H, 3.9. 1H NMR (CD2Cl2): δ 7.05, 6.54 (A andBB′ parts of an ABB′ spin systems, 3 H, C5H3), 1.46 (s, 9 H,NtBu), 1.08 (s, 3 H, SiMe2), 0.78 (s, 3 H, SiMe2). 13C{1H} NMR(CDCl3): δ 145.4 (s, C5H3 â), 121.8 (s, C5H3 R), 108.1 (s, C5H3

ipso), 77.2 (s, NCMe3), 28.7 (s, NCMe3), -0.45 (s, SiMe2), -1.81(s, SiMe2).Preparation of trans-5c. This complex was obtained (0.14

g, 54%) as cis-5c from NtBuH2 (0.17 mL, 1.61 mmol), trans-2c(0.24 g, 0.27 mmol), and PCl5 (0.11 g, 0.54 mmol) by theprocedure described for cis-5c. Anal. Calcd for C22H36-N2Si2Cl6W2: C, 27.4; N, 2.9; H, 3.8. Found: C, 27.6; N, 2.9;H, 3.9. 1H NMR (CD2Cl2): δ 6.69, 6.64 (A and BB′ parts of anABB′ spin system, 3 H, C5H3), 1.45 (s, 9 H, NtBu), 0.81 (s, 6H, SiMe2). 13C{1H} NMR (CDCl3): δ 141.2 (s, C5H3 ipso), 121.5(s, C5H3 R) 107.9 (s, C5H3 â), 77.4 (s, NCMe3), 28.7 (s, NCMe3),-0.2 (s, SiMe2).Preparation of [{MoCl(µ-NtBu)}2{µ-(η5-C5H4)2SiMe2}]

(6). A solution of 5a (0.31 g, 0.42 mmol) in THF (50 mL) wasadded to a Na amalgam (0.039 g, 1.7 mmol). The solutionbecame green. The mixture was stirred for 1 day and thenfiltered; solvent was removed in vacuo. The oil obtained wasextracted into toluene/pentane (80 mL, 1:3) and the solventremoved in vacuo. Complex 6 was obtained as a green solid(0.20 g, 80%). Anal. Calcd for C20H32N2Cl2SiMo2: C, 40.6; H,5.5; N, 4.7. Found: C, 40.9; H, 5.5; N, 4.4. 1H NMR (C6D6):δ 6.55, 5.11 (AA′ and BB′ parts of an AA′BB′ spin system, 4H, C5H4), 1.69 (s, 9 H, NtBu), -0.51 (s, 3 H, SiMe2). 13C{1H}NMR (C6D6): δ 107.5 (s, C5H4), 107.4 (s, C5H4), 106.8 (s, C5H4),77.0 (s, NCMe3), 32.2 (s, NCMe3), -3.4 (s, SiMe2).Preparation of [{MoO(µ-NtBu)}2{µ-(η5-C5H4)2SiMe2}]-

(Mo-Mo) (7). HgO (0.37 g, 1.7 mmol) was added to a solutionof 5 (0.40 g, 0.68 mmol) in THF (50 mL). The green solutionslowly became orange, and a white-gray precipitate appeared.The mixture was stirred for 1 day and then filtered, and thesolvent was removed in vacuo. The orange solid was Soxhletextracted with pentane. Complex 7 was obtained as a yellowmicrocrystalline solid (0.22 g, 59%). Anal. Calcd for C20-H32N2O2SiMo2: C, 43.5; H, 5.8; N, 5.1. Found: C, 43.3; H,

5.7; N, 5.0. IR (Nujol): ν(ModO) 876 s. 1H NMR (C6D6): δ6.50, 5.96 (AA′ and BB′ parts of an AA′BB′ spin system, 4 H,C5H4), 1.73 (s, 9 H, NtBu), -0.22 (s, 3 H, SiMe2). 13C{1H} NMR(CDCl3): δ 114.1 (s, C5H4), 108.2 (s, C5H4), 93.8 (s, C5H4), 67.8(s, NCMe3), 32.8 (s, NCMe3), -3.2 (s, SiMe2).Crystal Structure of 7. A suitable sized orange crystal

of 7 was obtained by crystallization from CH2Cl2/hexane. Thecrystal was mounted in a ENRAF-NONIUS CAD-4 automaticfour-circle diffractometer. Crystallographic and experimentaldetails are summarized in Table 2. Data were collected atroom temperature. Intensities were corrected for Lorentz andpolarization effects in the usual manner. No absorption orextinction corrections were made. The structure was solvedby a combination of heavy atom and direct methods andFourier synthesis.20 The structure was refined on F by full-matrix least-squares calculations. All non-hydrogen atomswere refined anisotropically. The hydrogen atoms were in-troduced from geometrical calculations and refined with fixedthermal parameters (U ) 0.08 Å2) using a riding model. Full-matrix least-squares refinement21 on F2 for all data and 385parameters converged to wR2 ) 0.104 (all data), conventionalR ) 0.038 (observed data), and GOF ) 0.994. The functionminimized was ∑w(Fo

2 - Fc2)2, w ) 1/[σ2(Fo

2) + (0.0786P)2 +4.7828P], where P ) (Fo

2 + 2Fc2)/3 and σ was obtained from

counting statistics. Anomalous dispersion corrections andatomic scattering factors were taken from ref 22.

Acknowledgment. We gratefully acknowledge fi-nancial support from the Comision Asesora de Investi-gacion Cientıfica y Tecnica (ref no. PB92-0178-C) andfrom the Universidad de Alcala de Henares (001/95).

Supporting Information Available: For 7, tables ofpositional parameters and U values for non-hydrogen atoms,positional parameters and U values for hydrogen atoms, andanisotropic displacement parameters (3 pages). Orderinginformation is given on any current masthead page.OM950943I

(20) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.(21) Sheldrick, G. M. SHELX93; University of Gottingen, 1993.(22) International Tables for X-Ray Crystallography; Kynoch

Press: Birmingham, England, 1974; Vol. IV.

Table 2. Crystallographic Data for 7

formula C20H32Mo2N2O2Sicryst habit prismaticcolor yellowsymmetry monoclinic, Pnunit cell determn least-squares fit from

25 reflcnsunit cell dimensa-c, Å 14.989(3), 9.885(2), 15.524(3)â, deg 94.72(3)packingV, Å3; Z 2292(1); 4Dcalcd, g cm-3 1.601Mr 552.4F(000) 1120µ, cm-1 11.63technique four-circle diffractometer;

bisecting geometry,graphite-orientedmonochromator; Mo KRω-θ scans; θ, 2-25°

no. of rflnsmeasd 4295indep obsd 4219

range of hkl h, 0 to 17; k, 0 to 11;l, -18 to +18

std rflns 2 reflcns every 120 min;no variation

R1 ) ∑(|Fo| - |Fc|)/∑|Fo| 0.038wR2 ) [∑w(Fo2 - Fc2)2/∑w(Fo2)2]1/2 0.104goodness of fit indicator on F2 0.966max peak in final diff map, e/Å3 0.803min peak in final diff map, e/Å3 -0.781

Imido Complexes of Molybdenum and Tungsten Organometallics, Vol. 15, No. 8, 1996 2107